I've seen that too. Laurie very nearly broke a mans thumb at a Halloween party over this very issue. She told him once clearly and politely that she was not interested and he persisted. Laurie used to be an auxiliary officer for our local police dept and has had the self defence training. she grabbed his thumb and twisted till he whimpered.
We've been active in the lifestyle for a few months and know dozens of great couples. Of all the women I know, other than Laurie, there are exactly 2 women who I would feel comfortable putting my hands on. Even with those 2 I would probably start with a back rub and check for reaction. If the lady I'm paying attention to gives a positive reaction to that I'll move on from there. If not I haven't really stepped over the line into rudeness.
I know I'm truly annoyed when I see Laurie having to deal with rude and unwelcome advances so i wont do that to anyone else. It's just politeness.
As for house parties, there are different sorts. Laurie and I attend a party that is very low pressure. Mr. almost broken thumb was asked not to come back.
At our party there is no public play usually. There are private bedrooms upstairs for that. The party games are non contact types. The big Halloween party game was bobbing for goodies. There were gummi boobies and dicks in a big bowl of water and you tried to suck one up with a straw.
Another house party we WONT be going back to was simply walk in, get naked, and start humping.
Not our kind of thing. You might have to look around a bit to find one that fits, but I'm sure glad we did.